FIG. 1 is a diagram of a heterogeneous network wireless communication system 100 including a macro base station and a micro base station. In this specification, a terminology of a heterogeneous network means a network in which the macro base station 110 and micro base stations 121/122 co-exist although an identical Radio Access Technology (RAT) is used.
The macro base station 110 means a general base station of a wireless communication system having a wide coverage and high transmit power. The macro base station may be called a macro cell.
For instance, the micro base station 121/122 can be called a micro cell, a pico cell, a femto cell, a home eNB (HeNB), a relay, or the like. The micro base station 121/122 is a small version of the macro base station 110 and can operate independently in a manner of performing most of functions of the macro base station. The micro base station is sort of a base station installed (overlay) in an area covered by the macro base station or the base station installable (non-overlay) in a radio shadow area where the macro base station is not able to cover. Compared to the macro base station 110, the micro base station 121/122 can accommodate small numbers of user equipments with a narrower coverage and lower transmit power.
A user equipment 131 can be directly served from the macro base station 110 (hereinafter a macro UE) and a user equipment 132 can be served from the micro base station 122 as well (hereinafter a micro UE). In some cases, the user equipment 132 existing in the coverage of the micro base station 122 may be served from the macro base station 110.
According to whether an access restriction is applied to a user equipment, the micro base station can be classified into two types. A first type corresponds to a Closed Subscriber Group (CSG) micro base station and a second type corresponds to an Open Access (OA) or an Open Subscriber Group (OSC) micro base station. The CSG micro base station can serve permitted specific user equipments and the OSG micro base station can serve all user equipments without any separate access restriction.